The present invention relates to an improved apparatus and method for filling the propellant chamber of an implantable pump. In particular, the present invention relates to an improved propellant bag or pillow for use in introducing propellant into the propellant chamber of an implantable pump, as well as methods of utilizing same.
Implantable pumps have been well known and widely utilized for many years. Typically, such devices are implanted into patients who require the delivery of active substances or medicaments to specific areas of their body. For instance, patients who are experiencing severe pain may require pain killers daily or multiple times per day. Absent the use of an implantable pump or the like, a patient of this type would be subjected to one or more painful injections of medication multiple times during the course of the day. In the case of pain associated with more remote areas of the body, such as the spine, these injections may be extremely difficult to administer and particularly painful for the patient. Moreover, attempting to treat conditions like these through oral or intravascular administration of medication often requires higher doses of medication that may cause severe side effects. Thus, it is widely recognized that utilizing an implantable pump may be beneficial to both the patient and the treating physician.
Many implantable pump designs have been proposed, including pumps employing mechanical means for and gas pressure driven propellant means for expelling fluids from the pump. The present invention is directly related to the latter. More particularly, the apparatus and methods taught in the present application are capable of being utilized with many different types of gas driven pumps, such as those shown in U.S. Pat. Nos. 4,969,873; 5,085,656; 5,336,194; 5,836,915; 5,722,957; 5,814,019; 5,766,150; and 6,730,060, as well as U.S. Patent Application Publication Nos. 2006/0259015, 2006/0259016, 2006/0271021, 2006/0271022, 2007/0005044, and 2007/0112328. The disclosures of each of the above-noted patents and patent applications are hereby incorporated by reference herein, and certain of these references may be referred to throughout the present application.
In general, gas driven implantable pumps, like each of the above-noted patents and patent applications, utilize an expandable propellant (e.g., an isobarically expanding gas) that acts upon a membrane to push medicament or other fluid from the pump. A common problem with such pumps, which have existed for some time, revolves around the filling of the propellant chamber with propellant. Above-noted U.S. Pat. No. 5,766,150 (“the '150 patent”) discloses an apparatus and method for use in such a filling process. As is shown in FIG. 1 of the '150 patent (reprinted as FIG. 1 of the present case), that patent teaches the use of a propellant pillow 13, which is filled with a gas propellant and placed into a propellant chamber 7 of an implantable pump. The chamber is thereafter sealed. FIG. 2 shows pillow 13 in greater detail, in particular the fact that the pillow includes a propellant bag 15 and septum 17 affixed to the bag, which are not labeled as such in the '150 patent. Because bag 15 consists of a material through which the propellant may diffuse (i.e., a permeable material), the gas slowly diffuses through the wall of the pillow and into chamber 7. Thus, the use of pillow 13 allows time for the propellant chamber and the remainder of the pump to be assembled before the gas escapes therefrom.
During assembly of a pump utilizing the device and methods taught in the '150 patent, the assembly steps first include punching bag 15 from an air padded foil or the like, evacuating it of all gases, and subsequently refilling it with a propellant. These steps generally involve the use of at least one cannula, needle, or syringe 19 that pierces self-sealing silicone septum 17 to both evacuate all gases and introduce propellant. After being filled, pillow 13 is then introduced into a pump that has been divided into propellant chamber 7 and a fluid/medicament storage chamber 6. Subsequent to inserting pillow 13 into propellant chamber 7 of the pump, that chamber is sealed and evacuated of all gases. This allows the propellant to slowly permeate through the walls of bag 15 and into propellant chamber 7. This method is generally applicable to any gas pressurized implantable pump, including the ones described in the various prior art references listed above. It has also been found that when a heat procedure is utilized to seal a propellant chamber like chamber 7, bags like bag 15 are caused to erupt (with one or more holes), thereby causing the propellant to more quickly fill the chamber.
While the device and methods taught in the '150 patent has been utilized for some time in filling implantable pumps such as those disclosed above, it is not without its drawbacks. For instance, the initial evacuation of and subsequent filling of propellant within pillow 15 sometimes results in the structure of the bag being damaged by the syringe(s) 19. More particularly, evacuation of gas from bag 15 (i.e., creating a vacuum) causes the walls of the bag to collapse upon themselves and sometimes into contact with the point of the syringe(s). This may result in the walls being pierced, which thereby leads to a faster escape of the propellant from bag 15 than is desired. Thus, while the '150 patent suggests placing the pillow within a sealed propellant chamber in approximately two minutes, this time period is significantly reduced when the bag walls are damaged. More often than not, this damage to pillow 13 results in less propellant ultimately being contained within the propellant chamber.
Therefore, there exists a need for an improved pillow for use in an improved method of filling the propellant chamber of an implantable pump.